Poll based cache event notifications in a distributed cache

ABSTRACT

Systems and methods that supply poll based notification system in a distributed cache, for tracking changes to cache items. Local caches on the client can employ the notification system to keep the local objects in sync with the backend cache service; and can further dynamically adjust the “scope” of notifications required based on the number and distribution of keys in the local cache. The server can maintain the changes in an efficient fashion (in blocks) and returns the changes to clients that perform the appropriate filtering. Notifications can be associated with a session and/or an application.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/108,526 filed on 26 Oct. 2008 entitled “POLL BASED CACHE EVENTNOTIFICATIONS IN A DISTRIBUTED CACHE”, the entirety of this applicationis hereby incorporated by reference. This non-provisional applicationfurther relates to U.S. patent application Ser. No. 12/363,505 filed on30 Jan. 2009, entitled “DISTRIBUTED CACHE ARRANGEMENT” and U.S. patentapplication Ser. No. 12/420,364 filed on 8 Apr. 2009, entitled“REPLICATION FOR COMMON AVAILABILITY SUBSTRATE” all of theaforementioned patent applications are incorporated herein by referencein their entireties.

BACKGROUND

Increasing advances in computer technology (e.g., microprocessor speed,memory capacity, data transfer bandwidth, software functionality, andthe like) have generally contributed to increased computer applicationin various industries. Ever more powerful server systems, which areoften configured as an array of servers, are often provided to servicerequests originating from external sources such as the World Wide Web,for example.

Typically, a continuing problem in computer systems remains handling ofthe growing amount of information or data available. The sheer amount ofinformation being stored on disks or other media for databases in someform has been increasing dramatically. While files and disks weremeasured in thousands of bytes a few decades ago, now databases of amillion megabytes (terabytes) and even billions of megabytes are beingcreated and employed in day-to-day activities.

Furthermore, today applications run on different tiers, in differentservice boundaries, and on different platforms (e.g. server, desktop,devices). For example, in a typical web application, many applicationsreside on a server supporting a large number of users; however, someclient components of the application can run on desktops, mobiledevices, and web browsers, and the like. In addition, advances inconnectivity and cheap storage combined with the complexity of softwaremanagement facilitate on-line services and software-as-a-service. Insuch services models, applications (and their data) are hosted incentral data centers (e.g., referred to as the “cloud”) and areaccessible and shared over the web.

The distributed applications require support for large number of users,high performance, throughput and response time. Such servicesorientation also requires the cost of service to be low, therebyrequiring the scalability and performance at low cost.

A further challenge in implementing storage systems is support fordistribution and heterogeneity of data and applications. Applicationsare composing (e.g. mashups) data and business logic from sources thatcan be local, federated, or cloud-based. Composite applications requireaggregated data to be shaped in a form that is most suitable for theapplication. Data and logic sharing is also an important requirement incomposite applications.

As explained earlier, data/applications can reside in different tierswith different semantics and access patterns. For example, data inback-end servers/clusters or in the cloud tends to be authoritative;data on the wire is message-oriented; data in the mid-tier is eithercached data for performance or application session data; and data on thedevices can be local data or data cached from back-end sources. With thecosts of memory falling, considerably large caches can be configured onthe desktop and server machines. With the maturity of 64-bit hardware,64-bit CPUs are becoming mainstream for client and server machines. True64-bit architectures support 64-bit CPUs, data or address buses, virtualaddressability and dramatically increase memory limits (to 264 bytes).Operating systems (e.g. Windows, Linux) are also upgraded to support andtake advantage of 64 bit address-space and large memories.

For example, desktops can be configured with 16 GB RAM, and servers canbe configured with up to 2 TB of RAM. Large memory caches allow for datato be located close to the application, thereby providing significantperformance benefits to such applications. In addition, in a world wherehundreds of gigabytes of storage is the norm, the ability to work withmost data in memory (large caches), and readily shift such data fromtables/trees to graphs of objects is the key to programmer productivityfor next generation applications. Moreover, supplying notifications toclients for continuously changing data in a highly available storeremains inefficient, and cannot be readily tailored to requirements ofan application.

SUMMARY

The following presents a simplified summary in order to provide a basicunderstanding of some aspects described herein. This summary is not anextensive overview of the claimed subject matter. It is intended toneither identify key or critical elements of the claimed subject matternor delineate the scope thereof. Its sole purpose is to present someconcepts in a simplified form as a prelude to the more detaileddescription that is presented later.

The subject innovation provides for a poll based notification componentthat tracks changes for items cached in a distributed store, viaemploying filtering sub-systems at different levels, to dynamicallyadjust scope of notifications (e.g., to a key level, a region level, anda cache level based on number of keys that tracking is desired thereon).Typically, in such distributed store data can be distributed orpartitioned amongst the various instances, wherein each instance can beresponsible for a set of partitions of data and referred to as the“primary” node for those data partitions. In addition, there can existone or more backups being kept for each partition also spread across thecache. Such instances hold the backup partitions, which can be referredto as secondary nodes.

A partition can also represent a range of ids that are mapped todifferent nodes. Moreover, regions and keys can be hashed to an ID,wherein keys are then hashed to a region that is further hashed to aspace id. The ID can then determine which partition it maps to (based onthe id range of the partition), for mapping to a node, for example.

Based on items to be stored, types of regions in form of region anddefault can be defined—wherein for all data items keys are obtained andhashed identifications mapped into partitions in form of key ranges.Such partitions can further be taken and spread onto different machinesthat form the distributed store.

In a related aspect, the distributed store can include a plurality ofnetworked machines or cluster of nodes that employ a Common AvailabilitySubstrate (CAS) for data transport/consistency operations; hencerendering the distributed store scalable and available. Such CAS canfurther supervise join/leave operations for nodes that in part form thedistributed store (e.g., monitoring health of nodes, managing lifecycles of nodes, creating a primary node on another machine).Accordingly, a server can efficiently maintain changes to cached data(e.g., in forms of blocks) and further return changes to clients, andhence monitor such changes at each of the designated levels. Thenotification component can further be included on the server and/orclient side, wherein the client can poll the necessary servers in thepartitioned cache.

In a related aspect, the notification component can include a selectioncomponent that optimizes operations via designating a subset ofnodes/servers based on partitions and keys positioned therein—whereinproviding notifications can be limited to such designated partitions.The client can register for notifications on changes to the named cache,region or a specific key, for example. Furthermore, the local cache onthe client can employ the notification component to keep the localobjects in sync with the backend cache service.

According to a further aspect, the notification component can spreadacross the client and server process spaces. On the server side, thenotification component can further include a notification manager unitas part of the notification system, to generate notification events forthe operations occurring on the cache items and regions (for whichnotifications are requested.) The notification manager unit can furtherarrange the notifications such that they are readily pulled by theclients. Moreover, on the client side, the notification subsystem andnotification registration requests can be stored in a sorted type (e.g.,dictionary like) structures. Such an arrangement can also containnotification requesting threads that periodically pulls thenotifications from the cache server.

In another aspect, each update operation performed obtains a uniquesequence number represented by the Logical Sequence Number (LSN)associated with a partition. Such LSN can be generated as part of areplication process (e.g., by noting the current sequence number foroperations before the enumeration is begun; and typically returningthose items in the partition wherein associated LSN is less than thestart LSN), and can be employed to determine the order of the operationswithin a partition. A partition can also represent a range of ids thatare mapped to different nodes. Moreover, regions and keys can be hashedto an ID, wherein keys are then hashed to a region that is furtherhashed to a space id. The ID can then determine which partition it mapsto (based on the id range of the partition), for mapping to a node, forexample. It is to be appreciated that other queues independent of thereplication process can also be employed.

According to a further aspect of the polling approach, the client cankeep track of the change sequence number (e.g., the LSN) per partition.When a user registers a key level notification, such can be translatedinto the partition that the key belongs to, followed by looking up thecurrent LSN on that partition and a storing thereof on the client side.Hence, a next time the “polling” component needs to poll, the machinethat contains such partition is also polled to return all events fromthe LSN being stored. For example, if the client is aware that forPartition P1 and the last LSN is 20, next time a polling componentproceeds around, it will send a request to a node containing partitionP1 and the Last seen LSN (20). Subsequently, the server responds backwith the list of events that is known since LSN 20. The client can thenupdate its last LSN to the latest LSN it has observed. Moreover, theserver can also be optimized to store the lists in a compressed format.

In a related aspect, the server side filtering can also be employed toimprove performance. If there exists a large number of operations andthe client is interested in very few operations (e.g., a single key whenthere has been numerous changes to a partition), then it can beefficient for the client to perform filtering on the server. As such,the server can apply the simple filters on the queue before returningthe event list to the client. The client-server communication can alsobe optimized by the client sending a group of partition requests to eachserver in parallel. The cache level notifications enable the clients tolisten to changes for all keys and regions being performed on the cache.The regions being added or deleted can also be considered a cache event.Such allows the applications to use “regions”, which are containers asfirst class objects and track their creation and deletion.

It is to be appreciated that the local cache can contain any number ofkeys. As such, by subscribing to the suitable or “right” level ofnotification, the subject innovation can significantly improveperformance. The local cache can subscribe to the notification system tolisten to key level changes. If the number of keys in a partitionexceeds a predetermined threshold, it subsequently switches to employingpartition level notification. Similarly if the number of keys in apartition falls below a threshold it will drop to using key levelnotification. Moreover, if notification misses occur, the local cachewill purge itself to avoid inconsistent data.

To the accomplishment of the foregoing and related ends, certainillustrative aspects of the claimed subject matter are described hereinin connection with the following description and the annexed drawings.These aspects are indicative of various ways in which the subject mattermay be practiced, all of which are intended to be within the scope ofthe claimed subject matter. Other advantages and novel features maybecome apparent from the following detailed description when consideredin conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of a notification system in adistributed cache in accordance with an aspect of the subjectinnovation.

FIG. 2 illustrates a particular notification system that furtherincludes a selection component according to a further aspect of thesubject innovation.

FIG. 3 illustrates a particular notification system that interacts witha plurality of caches according to a further aspect of the subjectinnovation.

FIG. 4 illustrates an exemplary layering arrangement according to afurther aspect of the subject innovation.

FIG. 5 illustrates a further methodology of designating a subset ofnodes/servers based on partitions and keys positioned therein.

FIG. 6 illustrates a methodology of adjusting a scope of notificationaccording to an aspect of the subject innovation.

FIG. 7 illustrates a key mapping for ranges of data when mapped to nodeson a distributed store.

FIG. 8 illustrates a particular layering arrangement for a distributedcache according to a particular aspect of the subject innovation

FIG. 9 illustrates an inference component in form of an artificialintelligence component that can be employed to facilitate notifications.

FIG. 10 illustrates an exemplary environment for implementing variousaspects of the subject innovation.

FIG. 11 illustrates a sample computing environment that can be employedfor replicating cache according to an aspect of the subject innovation.

DETAILED DESCRIPTION

The various aspects of the subject innovation are now described withreference to the annexed drawings, wherein like numerals refer to likeor corresponding elements throughout. It should be understood, however,that the drawings and detailed description relating thereto are notintended to limit the claimed subject matter to the particular formdisclosed. Rather, the intention is to cover all modifications,equivalents and alternatives falling within the spirit and scope of theclaimed subject matter.

FIG. 1 illustrates an exemplary notification system 100 according to anaspect of the subject innovation. The notification system 100 can be apoll based notification system that tracks changes to items cached in adistributed store 123 (e.g., a plurality of networked machines orcluster of nodes). Such notification system 100 can employ filtering atvarious levels, to dynamically adjust scope of notification (e.g., to akey level, a region level, a cache level, and the like)—based on numberof keys that tracking is desired thereon. Accordingly, the server canefficiently maintain changes (e.g., in forms of blocks) and furtherreturn changes to client/application 121, and hence monitor the changesat each of the designated levels.

The notification component 130 can further be spread across processspaces of the client 121 and server. On the server side, thenotification component 130 can generate the notification events for theoperations occurring on the cache items and regions, for whichnotifications are requested. It also arranges them such that they can bereadily pulled by the clients 121. On the client side 121, notificationregistration requests can be stored in a sorted (e.g., dictionary) likestructures. It also contains a notification requesting thread thatperiodically pulls the notifications from the cache server. Likewise, onthe server side, the notification component 130 responds to the clientrequest for CacheEvents for partitions it contains. In one exemplaryaspect, the notification component can take Notification Events directlyfrom CAS Replication queue.

In general, the CAS provides the distributed store 130 with datatransport and consistency operations to render the system 100 scalableand available, and further supervises join/leave operations for nodesthat in part form the distributed store 130 (e.g., monitoring health ofnodes, managing life cycles of nodes, creating a primary node on anothermachine).

As explained earlier, the notification system 100 can employ a pullbased model for notification as it can involve minimal changes to serverside. Moreover, the notification component 130 can provide an interfacefor the upper layers to register/unregister notification. On the clientside 121, such enables the server to store the client's notificationregistration requests and to deliver the notification events to theregistered clients in the order the notifications are generated.Likewise, on the server side such can collects and store notificationappropriately to be sent to the clients 121 on request.

In addition, the notification system 100 can be protocol agnostic, andhence need not presume particular network facility or protocol. Such canfacilitate operations when designing for push-based notifications, assuch push-based notifications are deemed considerably efficient ifmulti-cast protocol network is assumed.

According to a further aspect, the user can employ notifications throughtwo mechanisms, namely an explicit API and a session level API. Theexplicit API involves user registering the notifications with thedistributed store client. It is to be appreciated that registering withthe client does not imply that the notification metadata resides on theserver, and such can be handled transparently. For example for theapplication level API, there can exist two main classes—wherein thecache class includes the ability to register for cache events and theCacheEvent class is useful for managing the notifications. An exemplaryuser API can include:

  // Delegate Signature   public delegate voidDataCacheNotificationCallback(   string CacheName,   string regionName,  string key,    DataCacheItemVersion version,   DataCacheOperationcacheOperation,    DataCacheNotificationDescriptor nd);   EnumDataCacheOperation   {    AddItem = 0x1,    ReplaceItem = 0x2,   RemoveItem = 0x4,    AddRegion = 0x8,    RemoveRegion 0x10,   ClearRegion = 0x20,    EvictItem = 0x40,    ExpireItem = 0x80   }   // Region Level (use DEFAULT_REGION for the no-region case)   //   //The filter is a combination of CacheOperation types   e.g. Add | Replacewill   // call the callback for both Add and Replace operations.   //  // Methods on the DataCache class   public class DataCache   {  Public DataCacheNotificationDescriptor    AddCacheLevelCallback(DataCacheOperation filter,          DataCacheNotificationCallback clientCallback);   PublicDataCacheNotificationDescriptor     AddRegionLevelCallback(stringregion,         DataCacheOperation filter,        DataCacheNotificationCallback clientCallback);   PublicDataCacheNotificationDescriptor     AddItemLevelCallback(string key,        DataCacheOperation filter,         DataCacheNotificationCallbackclientCallback);   Public DataCacheNotificationDescriptor    AddItemLevelCallback(String key,         DataCacheOperation filter,        DataCacheNotificationCallback clientCallback,          Stringregion);    public void   RemoveCallback(DataCacheNotificationDescriptornotify);   // This is useful if the cache lost notifications -    // wecall this once per partition    public DataCacheNotificationDescriptor     AddFailureNotificationCallback(       DataCacheFailureNotificationCallback failureCallback);   // KeyLevel At the time of insertion   Cache.Put(,...,...,... int filter,CacheChangeDelegate   delegate);   //

Likewise, for session level APIs, the subject innovation can supportsession level notifications, wherein the notifications can be suppliedwith a session state that can further be reused. The CacheEvent objectis serializable and can be stored along with other session state. Whenthe session moves to a different machine, the application shouldre-register the notification on that machine using the registereventact.

Moreover, for local cache invalidations, the local cache implementationcan employ the notification subsystem, if configured, on the client toregister to listen for changes to the regions (partitions) that it caresfor and then employs such to invalidate the objects. It will filter forReplace/Remove/Evict/DeleteRegion operations only.

In one aspect, the Cache items maintains the Logical Sequence Number(LSN) (along with a simple time of creation of the partition (epoch)) asthe version number. The LSNs can typically be generated at the partitionlevel and reused for the replication protocol—wherein the reuse of theLSNs guarantees monotonically increasing versions and also makescomparisons easy to provide snapshot semantics.

In addition, change notifications can be sequentially tracked usingthese LSNs. The LSNs supplied for notifications can have empty slots dueto messages that are required for replication but not required fornotifications (e.g. control messages). Such can be handled by employingdummy notifications. The state of the client can be managed by keepingthe last notification LSN that the client read. Such state can also bekept on the client or on the server.

FIG. 2 illustrates a particular notification system 200 according to afurther aspect of the subject innovation—wherein the notificationcomponent 230 can further include a selection component 240 thatdesignates a subset of nodes/servers based on partitions and keyspositioned therein. Such subset of nodes servers can include primarynodes 1 to m, where m is an integer—wherein the primary nodes canrepresent most updated version of data), and secondary nodes (1 to n,where n is an integer), to represent backup for the data. By designatinga subset of servers to poll—as opposed to polling all servers uponoccurrence of a change—tracking operation can be optimized.

The client 221 can register/de-register for notifications interested in.Moreover, when events occur that clients 221 have shown interesttherein, associated delegates can be called. In addition, the servertypically does not maintain a client state—hence minimizingchange/processing. On the server side, a notification manager unit (notshown) associated with the notification component 230 can responds tothe client request for CacheEvents for partitions it contains. Suchnotification manager unit can further take Notification Events directlyfrom a queue associated with common availability substrate (CAS)Replication, which represents operations for data transport/consistency,to render the distributed store scalable and available.

According to a further aspect, on the server side, the notificationmanager unit responds to the client request for CacheEvents forpartitions it contains. Moreover, the notification manager unit can takeNotification Events directly from a replication subsystem, employed forreplicating data for high availability or other purposes. Moreover, eachupdate operation performed can obtain a unique sequence numberrepresented by the Logical Sequence Number (LSN) associated with apartition. Such LSN can be generated as part of a replication process(e.g., by noting the current sequence number for operations before theenumeration is begun; and typically returning those items in thepartition wherein associated LSN is less than the start LSN), and can beemployed to determine the order of the operations within a partition. Apartition can also represent a range of ids that are mapped to differentnodes. Furthermore, regions and keys can be hashed to an ID, whereinkeys are then hashed to a region that is further hashed to a space id.The ID can then determine which partition it maps to (based on the idrange of the partition), for mapping to a node, for example.

In a further aspect of the polling approach, the client can keep trackof the change sequence number (e.g., the LSN) per partition. When a userregisters a key level notification, such can be translated into thepartition that the key belongs to and then lookups the current LSN onthat partition and store it on the client side. Accordingly, the nexttime the “polling” component needs to poll, the machine that containssuch partition is also polled to return all events from the LSN beingstored. For example, if the client 221 is aware that for partition P1,the last LSN is 20, then the next time the polling component proceedsaround, it will send the request to the node containing partition P1 andthe Last seen LSN (20). Subsequently, the server responds back with thelist of events that is known since LSN 20. The client then updates itslast LSN to the latest LSN that it has observed. Moreover, the servercan also be optimized to store the lists in a compressed format. Forexample, instead of maintaining a separate list of changes it can:

a) obtain it from the replication queue that is already maintained forthe purposes of availability and load balancing; wherein memory and thequeue is reused; and/or

b) Compress the list into cache event blocks. Such cache event blockscan include start and end LSN noted on them. For example, when a clientrequests for a notification starting from LSN having number 20 and theserver has a block starting from 15-30, it will send the block. Hence,the client can ignore the events from 15-20 and process the remainder.It is to be appreciated that such queue can also remain independent ofthe replication queue, and be independently defined, wherein the queuemaintains track of all changes occurring. The changes can furtherinclude maintaining track of key operations and/or new value/old valueof data.

Accordingly, by maintaining cache events as blocks, one can save onmemory and scale the processing, since the network bandwidth usage alsobecomes lower. Moreover, different blocks can be maintained—for adds,removes and updates so that clients can request the appropriate eventand obtain them efficiently, and mitigate excessive messages. In arelated aspect, the server side filtering can also be employed toimprove performance. If there exists a large number of operations andthe client is interested relatively few operations (e.g., a single keywhen there has been numerous changes to a partition), it becomes moreefficient for the client to perform filtering operation on the server.Hence, the server can apply the simple filters on the queue beforereturning the event list to the client. The client-server communicationcan also be optimized by the client sending a group of partitionrequests to each server in parallel. The cache level notificationsenable the clients to listen to changes to all keys and regions beingperformed on the cache. The regions being added or deleted can also beconsidered a cache event. Such allows the applications to employ“regions”, which are containers as first class objects and track theircreation and deletion.

It is to be appreciated that the local cache can contain any number ofkeys. As such, subscribing to the suitable or “right” level ofnotification can improve performance significantly. The local cachesubscribes to the notification system to listen to key level changes. Ifthe number of keys in a partition exceeds a certain threshold, then itswitches to using partition level notification. Similarly if the numberof keys in a partition falls below a threshold it will drop to using keylevel notification. Moreover, if notification misses occur, the localcache can purge itself to avoid inconsistent data.

FIG. 3 illustrates a particular notification system 300 that interactswith a plurality of caches according to a further aspect of the subjectinnovation. An application initially registers to receive notificationsfor key A and key B. Such registration by the application indicates thatwhenever key A or key B changes, the application should be notifiedaccordingly. In general, such notification can be either a pull or apush notification, wherein items can be registered and if the data itemschanges—a poll can be performed periodically. When a cache item changes,the application is notified accordingly.

In the pull based model, the client polls the server to ask for changessimilar to Really Simple Syndication (RSS) Feeds. In the push basedsystem model, the server “pushes” information to the registered clients.Both system models are useful for different scenarios. Pull based systemmodel is scalable for large number of clients as the server need notmaintain state about the clients—yet it can increase the network trafficload as the clients have to poll all the servers. In addition, the pullbased model can be a waste of network resources if there are very fewchanges happening to the data. The push based model is efficient ifthere exists infrequent changes to data and if the user desires thechanges to be available as soon as they are made (a disadvantage beingthat the server needs to keep track of the client state and whatnotifications each client has received.)

The notifications can either be sent in order or can be out of order ifparallel processing is required. Moreover, such notifications caninclude the operations or the data as well—wherein the tracked changescan either be cumulative or net change (as in the current data not allthe changes that took place to arrive at this data) or include asequential list of changes. Both pull and push can guarantee ordering,wherein on the client side, the delegates can be called in sequence.

Regardless of push/pull mechanism, filtering can be performed either onthe client or on the server. For example, Client side filtering enablesthe server to be free of state. Such can be advantageous if there areeither few changes on the server or if the client registers for allchanges. Moreover, Server side filtering can be deemed more efficient ifthe client registers for few changes (particularly for predeterminedkeys).

In such client-server environment, the routing table maps the partitionkeys, to designate which keys live on which nodes. For example, therouting table can represent a subset of a partition map, wherein fordata items keys are obtained and hashed identifications are mapped intopartitions in form of key ranges. Initially the application 310 canrequest notification for keys “K1” and “K3”, wherein cache 1 serves asprimary for K1, V1; cache 2 serves as primary for K2, V2, and cache 3serves as primary for K3, V3. Subsequently, the routing table can mapkeys to partition ranges. Subsequently, nodes associated with suchnotification request can be polled, wherein such nodes can return listof changes, for example.

In the pull model, clients poll and pull the notifications from theservers. The user API remains similar to the push model, however, theclient of the distributed store can poll at frequent intervals.Exponential backoff mechanism can further be employed to ensure that onedoes not poll servers unnecessarily. Such intervals can be configuredand predetermined. Moreover, the client side maintains the last LSNobserved (if any), and subsequently asks the server for allnotifications after such LSN. If the server has enough log state, itreturns all notifications with LSN larger than the client LSN. If not,it can return an error.

Moreover, in the case of a local cache, if notifications are lost, thecache is purged. Likewise, if a cache notification is missed, then onecan raise the CacheFailure Notification calls to enable the user knowthat they missed some notifications for the set of regions. Each servercan maintain the data (e.g., the primary/secondary node) also maintainsthe notification logs. Such logs can be maintained by the CASreplication substrate. In case of the routing client, the clientexplicitly polls each server that it is interested in and obtains allnotifications for a partition. The client of the distributed storeaggregates all the requests and fetches the appropriate notifications.Subsequently, it filters and calls the appropriate delegates, wherein asimple filtering can be performed on the server side.

FIG. 4 illustrates an exemplary layering arrangement 400 according to afurther aspect of the subject innovation, which illustrates interactionbetween client and a server of a distributed store according to anaspect of the subject innovation. The polling component 435 can performthe actual polling and/or actual listening requests in case of push.Likewise, the filtering component 437 can be employed to check if agiven notification requires processing or not. Similarly, the dispatchmanager component 439 dispatches notification to the caller. In additionthe event queue 441 can maintain a list of events that have occurred.Such event queue 441 provides an API to obtain a list of events.Moreover, the queue can maintain cache events by employing the LSNorder, and the callers are expected to provide the last LSN to obtain alist of the next set of events. Furthermore, there can exist multipleinternal implementations for the Event Queue. One implementation canemploy the CAS replication queue 445 directly to fetch thenotifications.

In a related aspect, the queue can be a filtered event queue, and suchcan further facilitate operation when the filter is applied on theserver side—wherein the filter may or may not be persistent on theserver. The event queue can further be configured, such as sending amaximum number of notifications at any point (e.g., 100 or 1000)—so asto not overwhelm the client or message handlers. Moreover, the queue cansend out the LSN that it has, so that the client can re-poll the server.The queue can also report lost events, wherein if the caller asks forevents from LSN 10 and the queue only has events from LSN 12, then itreports such loss.

According to a further aspect, the polling component 435 can poll allthe servers at regular intervals and maintain the last LSN observed fora partition per named cache. Such polling component 435 can furtheremploy the CAS Client DLL to obtain list of partitions and servers andbatches requests, such that it requests the notifications for allpartitions that a server contains. The polling component 435 can furtherimplement exponential back off per partition/server.

The filtering component 437 can maintain hash tables of registeredrequests for cache level, region or key level events. The filteringcomponent 437 can have APIs for taking in a cache event and determine ifit is of interest. For example, in the client scenario described above,the polling component 435 can obtain a batch of events then calls thefiltering component to filter out the unnecessary ones. The remainingones can then be sent to the dispatch manager component 439.

Likewise, the dispatch manager component 439 can maintain a queue ofevents that needs to be dispatched. The dispatch can occur on a singlethread per partition—so as to guarantee sequential execution ofnotifications. The local cache can register itself as a client to thenotification system. Moreover, the local cache can register itself forthe entire cache and act on the events directly. Put differently, theserver side can maintain a list of cache events based on LSNs, and theclient polls each server to obtain an updated list of events that haveoccurred since the last poll. The client can further maintain filters tosend the event that is pertinent by the application (e.g., registeredthereby). As explained earlier, applications can also register delegatesfor notifications on any node which may be different from the primarynode on which the object resides.

Such layering arrangement 400 can further provide for a scalable systemthat can be tailored to different types of communication layers such asTCP/IP, and pluggable features can be further enabled for readilyadapting to a user's need. The distributed cache implementing thelayering arrangement 400 can dynamically scale itself with growth ofapplications associated therewith, by addition of additional computersas nodes to a cluster of machines. Moreover, a clustering substrate canestablish clustering protocols among the plurality of nodes that formthe single unified cache. For example, when a node is to join or leavethe cluster, requisite operation for adding or leaving the cluster aremanaged, wherein the distributed component availability substrate canemploy such information to manage operation (e.g., monitoring health ofnodes, managing life cycles of nodes, creating a primary node on anothermachine). In addition, for each node each of the components forming thelayering arrangement can be pluggable based on user needs, systemrequirements, and the like. It is to be appreciated that due topluggable features supplied by the layering arrangement, users can plugin different types of data managers tailored to users' requirements suchas; a transaction data manager or a disk paged data manager, and thelike.

In one aspect, the propagation of notifications can be managed in adistributed fashion, to include providing high availability for suchnotifications when the primary node fails. For example, such can behandled by maintaining a local lookup table indexed by delegate id onthe node where the application registers the delegate. The primary nodethat stores the object maintains the delegate id and the originatingnode information. When such object changes in the distributed store, theprimary node can notify all the originating nodes passing along thedelegate id.

Similarly, the lookup table can be employed to call the appropriatedelegate, thus providing the change information to the application in adistributed fashion. For example, notifications can be asynchronous andcan further be backed up using the same secondary nodes. Accordingly, inthe event of failures, the secondary nodes attempt to deliver thepending notifications.

FIG. 5 illustrates a methodology 500 of designating a subset ofnodes/servers based on partitions and keys positioned therein. While theexemplary method is illustrated and described herein as a series ofblocks representative of various events and/or acts, the subjectinnovation is not limited by the illustrated ordering of such blocks.For instance, some acts or events may occur in different orders and/orconcurrently with other acts or events, apart from the orderingillustrated herein, in accordance with the innovation. In addition, notall illustrated blocks, events or acts, may be required to implement amethodology in accordance with the subject innovation. Moreover, it willbe appreciated that the exemplary method and other methods according tothe innovation can be implemented in association with the methodillustrated and described herein, as well as in association with othersystems and apparatus not illustrated or described. Initially and at510, applications/data can be distributed throughout a distributedcache, wherein such distributed cache can be scaled depending on thechanging requirement of the applications and/or data. Next anapplication can request notifications for predetermined keys at 520.Subsequently and at 530 a subset of nodes that form the distributedcache can be designated based on partitions/keys positioned therein. At540, nodes associated with such notification request can be polled,wherein such nodes can return list of changes.

FIG. 6 illustrates a further methodology 600 of adjusting a scope ofnotification in accordance with an aspect of the subject innovation.Initially and at 610, a scope of notification can be specified, whereinsuch scope of notification can be set to a key level, a region level, acache level and the like, based on number of keys that tracking isdesired thereon. Accordingly, the client can register for notificationson changes to the named cache, region or a specific key. Furthermore,the local cache on the client can employ such notifications to keep thelocal objects in sync with the backend cache service.

Next and at 620 changes can be monitored at such designated levels asidentified by the client/application. Subsequently, and at 630 changescan be identified and the application notified accordingly. At 640, thescope of the notification can be adjusted to a different scope, andchanges tracked at such new level. Accordingly, a server can efficientlymaintain changes to cached data (e.g., in forms of blocks) and furtherreturn changes to clients, and hence monitor such changes at each of thedesignated levels.

FIG. 7 illustrates a key mapping 700 for ranges of data when mapped tonodes on a distributed store(s) 710, 712, 714. Based on items to bestored, such as in case of a toy delivery store for boxes correspondingto the toys, two types of regions in form of region and default can bedefined—wherein for all data items keys are obtained and hashedidentifications mapped into partitions in form of key ranges. Suchpartitions can further be taken and spread onto different machines thatform the distributed store 710, 712, 714. The partition maps can furtherinclude both global partition maps and local partition maps. The localpartition map can be placed on a node, to supply knowledge aboutpartitions placed on the node. Likewise, the global partition suppliesknowledge about all partition maps in the cluster of nodes that form thedistributed store. Furthermore, the local cache can maintain items inde-serialized object format and without involving the distributed store.Requests arriving in the local cache can then be synched with primarydata being held in the primary node.

FIG. 8 illustrates a particular layering arrangement 800 for adistributed cache according to a particular aspect of the subjectinnovation. Such layering arrangement enables aggregating memorycapacity of multiple computers into a single unified cache, according toan aspect of the subject innovation. As illustrated in FIG. 8, each ofthe cache nodes 831, 833 (1 to n, n being an integer) the layeringarrangement 800, which includes a data manager component 810, an objectmanager component 812 and a distributed object manager component 814—theset up which can be implemented in a modular fashion—wherein, thedistributed object manager component 814 is positioned on top of theobject manager component 812, which itself placed on top of the datamanager component 810. The data manager component 810 supplies basicdata functions (e.g., hash functions), and the object manager component812 implements object facade thereon including cache objects with thedistributed object manager component 814 providing the distribution. Assuch, the object manager component 812 and data manager component 810can act as local entities, wherein the distributed object managercomponent 814 performs the distributions. Moreover, a clusteringsubstrate can establish clustering protocols among the plurality ofnodes that form the single unified cache.

As explained earlier, the data manager component 810 (e.g., in memory)provides primitive high performance data structures such as hash tables,Btrees, and the like. Since such data manager 810 is memory bound andall operations of the distributed cache of the subject innovation areatomic, it can typically implement highly concurrent hash tables. Suchfurther facilitates creating the infrastructure for supplying containersand indexes on containers. In addition it provides simple eviction andexpiration on these hash structures. It is to be appreciated that due topluggable features supplied by the layering arrangement 800, users canplug in different types of data managers tailored to users' requirementssuch as; a transaction data manager or a disk paged data manager, andthe like. Likewise, the object manager component 812 provides the objectabstraction and implements the concept of named caches and region byemploying data structures provided by the data manager.

Similarly, the distributed object manager component 814 employs thelocal object manager and integrates with the Distributed Components 811to provide the abstraction of the distributed cache. Core to thedistributed cache of the subject innovation is the DistributedComponents/availability substrate 811 which provides the transport anddata consistency operations to make the system scalable and available.The object distribution component can optionally be implemented as partof a client tier to facilitate dispatching requests (e.g., directly) tothe nodes associated with the single unified cache.

In one particular aspect, the distributed object manager component 814can further include a Dispatch Manager component 817 and a distributedManager component 819. The Dispatch Manager component 817 can furtherlook up the routing table to dispatch the requests to a primary node(e.g., where a region is located) as part of dynamically scalabledistributed cache. Moreover, such dispatch manager component 817 can bealso present in the client so that the client can directly dispatchrequests to the primary node. For example, the distributed objectmanager 811 on the receiving node can interact with the partition map tocheck if the node is indeed designated as the primary node as part of aplurality of nodes associated with the distributed cache, and calls theObject Manager component 814 to perform the operation. In the case ofwrite operations, such distributed object manager component 814 can alsocommunicate with a replicator to replicate the data to the secondarynodes. It can also interact with the failover manager systems (notshown) to clone regions to create new secondary or primary nodes duringreconfiguration procedures subsequent to possible failures.

The object manager component 812 can further include a notificationmanagement component 823 that tracks changes to regions and objects andrelays notifications to delegates listening to those events. Moreover,applications can also register delegates for notifications on any nodewhich may be different from the primary node on which the objectresides. The distributed object manager component 814 can further managethe propagation of notifications in a distributed fashion includingproviding high availability for such notifications when the primary nodefails. For example, such can be handled by maintaining a local lookuptable indexed by delegate id on the node where the application registersthe delegate. The primary node that stores the object maintains thedelegate id and the originating node information. When such objectchanges in the distributed object manager component 814, the primarynode can notify all the originating nodes passing along the delegate id.

Similarly, the distributed object manager component 814 associated withthe receiver can employ the lookup table to call the appropriatedelegate, thus providing the change information to the application in adistributed fashion. For example, notifications can be asynchronous andcan further be backed up using the same secondary nodes. Accordingly, inthe event of failures, the secondary nodes attempt to deliver thepending notifications, wherein during the primary node failurenotifications can be resent—since the primary may not have synchronizedthe information regarding the delivered notifications before failure.Since all notifications carry the region, key and version information,application can use the version to ignore duplicate notifications.

Likewise, the Availability Substrate 811 provides scalability andavailability to systems that contain a storage component associated withthe distributed cache of the subject innovation. For example, theavailability substrate can include load balancers, fail over managers,replicators and the like. Interacting with such availability substrate811 is the communication substrate 809 that provides for failuredetection of nodes and reliable message delivery therebetween. Moreover,the communication substrate 809 provides the communication channels andcluster management. Such communication substrate 809 can providecallbacks whenever a new node joins the cluster or when a node dies orfails to respond to exchanged messages (e.g., heart beat messages).Moreover, the communication substrate 809 can provide efficientpoint-to-point and multicast delivery channels, and can further providereliable message delivery that is required for implementing thereplication protocols. For example, the communication substrate 809supports notifications by maintaining delegate information in cacheitems and triggering the notification when items are modified. Suchcomponent also triggers eviction based on policies defined at the regionor named cache level.

FIG. 9 illustrates an inference component in form of an artificialintelligence (AI) component 920 that can be employed to facilitatenotifying in the distributed cache and/or distribute applications. Forexample, the artificial intelligence component 920 can supply additionalanalysis with the distributed cache manager to improve distributionand/or scaling of the system. As used herein, the term “inference”refers generally to the process of reasoning about or inferring statesof the system, environment, and/or user from a set of observations ascaptured via events and/or data. Inference can be employed to identify aspecific context or action, or can generate a probability distributionover states, for example. The inference can be probabilistic-that is,the computation of a probability distribution over states of interestbased on a consideration of data and events. Inference can also refer totechniques employed for composing higher-level events from a set ofevents and/or data. Such inference results in the construction of newevents or actions from a set of observed events and/or stored eventdata, whether or not the events are correlated in close temporalproximity, and whether the events and data come from one or severalevent and data sources.

The AI component 920 can employ any of a variety of suitable AI-basedschemes as described supra in connection with facilitating variousaspects of the herein described invention. For example, a process forlearning explicitly or implicitly how or what candidates are ofinterest, can be facilitated via an automatic classification system andprocess. Classification can employ a probabilistic and/orstatistical-based analysis (e.g., factoring into the analysis utilitiesand costs) to prognose or infer an action that a user desires to beautomatically performed. For example, a support vector machine (SVM)classifier can be employed. Other classification approaches includeBayesian networks, decision trees, and probabilistic classificationmodels providing different patterns of independence can be employed.Classification as used herein also is inclusive of statisticalregression that is utilized to develop models of priority.

As will be readily appreciated from the subject specification, thesubject innovation can employ classifiers that are explicitly trained(e.g., via a generic training data) as well as implicitly trained (e.g.,via observing user behavior, receiving extrinsic information) so thatthe classifier is used to automatically determine according to apredetermined criteria which answer to return to a question. Forexample, with respect to SVM's that are well understood, SVM's areconfigured via a learning or training phase within a classifierconstructor and feature selection module. A classifier is a functionthat maps an input attribute vector, x=(x1, x2, x3, x4, xn), to aconfidence that the input belongs to a class—that is,f(x)=confidence(class).

The word “exemplary” is used herein to mean serving as an example,instance or illustration. Any aspect or design described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other aspects or designs. Similarly, examples areprovided herein solely for purposes of clarity and understanding and arenot meant to limit the subject innovation or portion thereof in anymanner. It is to be appreciated that a myriad of additional or alternateexamples could have been presented, but have been omitted for purposesof brevity.

Furthermore, all or portions of the subject innovation can beimplemented as a system, method, apparatus, or article of manufactureusing standard programming and/or engineering techniques to producesoftware, firmware, hardware or any combination thereof to control acomputer to implement the disclosed innovation. For example, computerreadable media can include but are not limited to magnetic storagedevices (e.g., hard disk, floppy disk, magnetic strips . . . ), opticaldisks (e.g., compact disk (CD), digital versatile disk (DVD) . . . ),smart cards, and flash memory devices (e.g., card, stick, key drive . .. ). Additionally it should be appreciated that a carrier wave can beemployed to carry computer-readable electronic data such as those usedin transmitting and receiving electronic mail or in accessing a networksuch as the Internet or a local area network (LAN). Of course, thoseskilled in the art will recognize many modifications may be made to thisconfiguration without departing from the scope or spirit of the claimedsubject matter.

Furthermore, all or portions of the subject innovation can beimplemented as a system, method, apparatus, or article of manufactureusing standard programming and/or engineering techniques to producesoftware, firmware, hardware or any combination thereof to control acomputer to implement the disclosed innovation. For example, computerreadable media can include but are not limited to magnetic storagedevices (e.g., hard disk, floppy disk, magnetic strips . . . ), opticaldisks (e.g., compact disk (CD), digital versatile disk (DVD) . . . ),smart cards, and flash memory devices (e.g., card, stick, key drive . .. ). Additionally it should be appreciated that a carrier wave can beemployed to carry computer-readable electronic data such as those usedin transmitting and receiving electronic mail or in accessing a networksuch as the Internet or a local area network (LAN). Of course, thoseskilled in the art will recognize many modifications may be made to thisconfiguration without departing from the scope or spirit of the claimedsubject matter.

In order to provide a context for the various aspects of the disclosedsubject matter, FIGS. 10 and 11 as well as the following discussion areintended to provide a brief, general description of a suitableenvironment in which the various aspects of the disclosed subject mattermay be implemented. While the subject matter has been described above inthe general context of computer-executable instructions of a computerprogram that runs on a computer and/or computers, those skilled in theart will recognize that the innovation also may be implemented incombination with other program modules.

As used in this application, the terms “component”, “system”, “engine”are intended to refer to a computer-related entity, either hardware, acombination of hardware and software, software, or software inexecution. For example, a component can be, but is not limited to being,a process running on a processor, a processor, an object, an executable,a thread of execution, a program, and/or a computer. By way ofillustration, both an application running on a server and the server canbe a component. One or more components can reside within a processand/or thread of execution, and a component can be localized on onecomputer and/or distributed between two or more computers.

Generally, program modules include routines, programs, components, datastructures, and the like, which perform particular tasks and/orimplement particular abstract data types. Moreover, those skilled in theart will appreciate that the innovative methods can be practiced withother computer system configurations, including single-processor ormultiprocessor computer systems, mini-computing devices, mainframecomputers, as well as personal computers, hand-held computing devices(e.g., personal digital assistant (PDA), phone, watch . . . ),microprocessor-based or programmable consumer or industrial electronics,and the like. The illustrated aspects may also be practiced indistributed computing environments where tasks are performed by remoteprocessing devices that are linked through a communications network.However, some, if not all aspects of the innovation can be practiced onstand-alone computers. In a distributed computing environment, programmodules may be located in both local and remote memory storage devices.

With reference to FIG. 10, an exemplary environment 1010 forimplementing various aspects of the subject innovation is described thatincludes a computer 1012. The computer 1012 includes a processing unit1014, a system memory 1016, and a system bus 1018. The system bus 1018couples system components including, but not limited to, the systemmemory 1016 to the processing unit 1014. The processing unit 1014 can beany of various available processors. Dual microprocessors and othermultiprocessor architectures also can be employed as the processing unit1014.

The system bus 1018 can be any of several types of bus structure(s)including the memory bus or memory controller, a peripheral bus orexternal bus, and/or a local bus using any variety of available busarchitectures including, but not limited to, 11-bit bus, IndustrialStandard Architecture (ISA), Micro-Channel Architecture (MSA), ExtendedISA (EISA), Intelligent Drive Electronics (IDE), VESA Local Bus (VLB),Peripheral Component Interconnect (PCI), Universal Serial Bus (USB),Advanced Graphics Port (AGP), Personal Computer Memory CardInternational Association bus (PCMCIA), and Small Computer SystemsInterface (SCSI).

The system memory 1016 includes volatile memory 1020 and nonvolatilememory 1022. The basic input/output system (BIOS), containing the basicroutines to transfer information between elements within the computer1012, such as during start-up, is stored in nonvolatile memory 1022. Byway of illustration, and not limitation, nonvolatile memory 1022 caninclude read only memory (ROM), programmable ROM (PROM), electricallyprogrammable ROM (EPROM), electrically erasable ROM (EEPROM), or flashmemory. Volatile memory 1020 includes random access memory (RAM), whichacts as external cache memory. By way of illustration and notlimitation, RAM is available in many forms such as synchronous RAM(SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rateSDRAM (DDR SDRAM), enhanced SDRAM (ESDRAM), Synchlink DRAM (SLDRAM), anddirect Rambus RAM (DRRAM).

Computer 1012 also includes removable/non-removable,volatile/non-volatile computer storage media. FIG. 10 illustrates a diskstorage 1024, wherein such disk storage 1024 includes, but is notlimited to, devices like a magnetic disk drive, floppy disk drive, tapedrive, Jaz drive, Zip drive, LS-60 drive, flash memory card, or memorystick. In addition, disk storage 1024 can include storage mediaseparately or in combination with other storage media including, but notlimited to, an optical disk drive such as a compact disk ROM device(CD-ROM), CD recordable drive (CD-R Drive), CD rewritable drive (CD-RWDrive) or a digital versatile disk ROM drive (DVD-ROM). To facilitateconnection of the disk storage devices 1024 to the system bus 1018, aremovable or non-removable interface is typically used such as interface1026.

It is to be appreciated that FIG. 10 describes software that acts as anintermediary between users and the basic computer resources described insuitable operating environment 1010. Such software includes an operatingsystem 1028. Operating system 1028, which can be stored on disk storage1024, acts to control and allocate resources of the computer system1012. System applications 1030 take advantage of the management ofresources by operating system 1028 through program modules 1032 andprogram data 1034 stored either in system memory 1016 or on disk storage1024. It is to be appreciated that various components described hereincan be implemented with various operating systems or combinations ofoperating systems.

A user enters commands or information into the computer 1012 throughinput device(s) 1036. Input devices 1036 include, but are not limitedto, a pointing device such as a mouse, trackball, stylus, touch pad,keyboard, microphone, joystick, game pad, satellite dish, scanner, TVtuner card, digital camera, digital video camera, web camera, and thelike. These and other input devices connect to the processing unit 1014through the system bus 1018 via interface port(s) 1038. Interfaceport(s) 1038 include, for example, a serial port, a parallel port, agame port, and a universal serial bus (USB). Output device(s) 1040 usesome of the same type of ports as input device(s) 1036. Thus, forexample, a USB port may be used to provide input to computer 1012, andto output information from computer 1012 to an output device 1040.Output adapter 1042 is provided to illustrate that there are some outputdevices 1040 like monitors, speakers, and printers, among other outputdevices 1040 that require special adapters. The output adapters 1042include, by way of illustration and not limitation, video and soundcards that provide a means of connection between the output device 1040and the system bus 1018. It should be noted that other devices and/orsystems of devices provide both input and output capabilities such asremote computer(s) 1044.

Computer 1012 can operate in a networked environment using logicalconnections to one or more remote computers, such as remote computer(s)1044. The remote computer(s) 1044 can be a personal computer, a server,a router, a network PC, a workstation, a microprocessor based appliance,a peer device or other common network node and the like, and typicallyincludes many or all of the elements described relative to computer1012. For purposes of brevity, only a memory storage device 1046 isillustrated with remote computer(s) 1044. Remote computer(s) 1044 islogically connected to computer 1012 through a network interface 1048and then physically connected via communication connection 1050. Networkinterface 1048 encompasses communication networks such as local-areanetworks (LAN) and wide-area networks (WAN). LAN technologies includeFiber Distributed Data Interface (FDDI), Copper Distributed DataInterface (CDDI), Ethernet/IEEE 802.3, Token Ring/IEEE 802.5 and thelike. WAN technologies include, but are not limited to, point-to-pointlinks, circuit switching networks like Integrated Services DigitalNetworks (ISDN) and variations thereon, packet switching networks, andDigital Subscriber Lines (DSL).

Communication connection(s) 1050 refers to the hardware/softwareemployed to connect the network interface 1048 to the bus 1018. Whilecommunication connection 1050 is shown for illustrative clarity insidecomputer 1012, it can also be external to computer 1012. Thehardware/software necessary for connection to the network interface 1048includes, for exemplary purposes only, internal and externaltechnologies such as, modems including regular telephone grade modems,cable modems and DSL modems, ISDN adapters, and Ethernet cards.

FIG. 11 is a schematic block diagram of a sample-computing environment1100 that can be employed for replicating cache according to an aspectof the subject innovation. The system 1100 includes one or moreclient(s) 1110. The client(s) 1110 can be hardware and/or software(e.g., threads, processes, computing devices). The system 1100 alsoincludes one or more server(s) 1130. The server(s) 1130 can also behardware and/or software (e.g., threads, processes, computing devices).The servers 1130 can house threads to perform transformations byemploying the components described herein, for example. One possiblecommunication between a client 1110 and a server 1130 may be in the formof a data packet adapted to be transmitted between two or more computerprocesses. The system 1100 includes a communication framework 1150 thatcan be employed to facilitate communications between the client(s) 1110and the server(s) 1130. The client(s) 1110 are operatively connected toone or more client data store(s) 1160 that can be employed to storeinformation local to the client(s) 1110. Similarly, the server(s) 1130are operatively connected to one or more server data store(s) 1140 thatcan be employed to store information local to the servers 1130.

What has been described above includes various exemplary aspects. It is,of course, not possible to describe every conceivable combination ofcomponents or methodologies for purposes of describing these aspects,but one of ordinary skill in the art may recognize that many furthercombinations and permutations are possible. Accordingly, the aspectsdescribed herein are intended to embrace all such alterations,modifications and variations that fall within the spirit and scope ofthe appended claims. Furthermore, to the extent that the term “includes”is used in either the detailed description or the claims, such term isintended to be inclusive in a manner similar to the term “comprising” as“comprising” is interpreted when employed as a transitional word in aclaim.

1. A computer implemented method comprising: employing a processor toexecute computer executable instructions stored on a computer readablemedium to perform the following acts: tracking changes to cached data ina distributed store via a filtering sub-system; and dynamicallyadjusting scope of notifications for tracked changes.
 2. The computerimplemented method of claim 1 further comprising notifying a client(s)of the distributed store regarding tracked changes based on polling acluster of nodes that form the distributed store.
 3. The computerimplemented method of claim 2 further comprising employing a CommonAvailability Substrate (CAS) to maintain availability of operations forthe distributed data store during the tracking act.
 4. The computerimplemented method of claim 3, the polling further comprising a pull orpush model for the distributed store.
 5. The computer implemented methodof claim 3, the tracking act further comprising maintaining track of:key operations; or values of data; or a combination thereof.
 6. Thecomputer implemented method of claim 3 further comprising trackingchange sequence numbers per partition.
 7. The computer implementedmethod of claim 3 further comprising maintaining cache events as blocksfor optimal transport or processing.
 8. The computer implemented methodof claim 3 further comprising propagating notifications when a primarynode of a partition fails.
 9. The computer implemented method of claim 2further comprising registering the client(s) for receiving notificationsfrom a named cache, or a region, or a key or a combination thereof. 10.The computer implemented method of claim 3 further comprising employinga routing table to correspond keys with nodes of the distributed store.11. The computer implemented method of claim 1 further comprisingimplementing a session based notification that associates a notifyingact with a session in the distributed store.
 12. A computer implementedsystem that facilitates tracking data changes in a distributed storecomprising: a processor; a memory communicatively coupled to theprocessor, the memory having stored therein computer-executableinstructions configured to implement the computer implemented systemincluding: a plurality of nodes that form a distributed store; and anotification component that tracks changes to data cached in thedistributed store based on a session or an application or a combinationthereof.
 13. The computer implemented system of claim 12, thenotification component further comprising a filtering system thatadjusts scope of notification.
 14. The computer implemented system ofclaim 12 further comprising a routing table that directs replicated datato a plurality of nodes that form the distributed store.
 15. Thecomputer implemented system of claim 12 further comprising a selectioncomponent that designates a subset of nodes or servers based onpartitions or keys partitioned therein.
 16. The computer implementedsystem of claim 12 further comprising a Logical Sequence Number (LSN)generated as part of a replication process associated with a CommonAvailability Substrate (CAS).
 17. The computer implemented system ofclaim 12 the distributed store further comprising a layering arrangementthat supplies an explicit aggregated cache for applications associatedtherewith, the layering arrangement includes: a distributed objectmanager component that facilitates abstraction of the explicitaggregated cache in a distributed environment, to a single unifiedcache; and an object manager component that manages policies associatedwith objects stored in each of nodes that form the single unified cache.18. The computer implemented system of claim 17 further comprising adata manager component that supplies storage data structures for theobjects.
 19. The computer implemented system of claim 17 furthercomprising a clustering substrate that establishes clustering protocolsbetween nodes that form the single unified cache.
 20. A computerimplemented system that facilitates tracking changes to cached datacomprising: means for managing consistency operations of data transferin a distributed store that is formed via a plurality of nodes; andmeans for tracking changes to data at different levels in thedistributed store.